1. Field of the Invention
The present invention relates to a loop holding device of a chain stitch sewing machine, and more particularly to a loop engaging device of a chain stitch sewing machine which continuously forms a loop stitch by a needle thread and a looper thread.
2. Description of the Related Art
A loop holding device of a sewing machine of this type shown in FIGS. 7 and 8 has been known.
The well-known chain stitch sewing machine can form both an over-edge chain stitch and a covering chain stitch.
FIG. 7 is a side view showing a cloth presser 10, and 10A denotes a support member which can be freely attached to and removed from the lower end of a presser rod which is not shown. 10B denotes a cloth presser and a shaft 10C in a horizontal direction thereof can be attached to and removed from the lower end of the support member 10A by means of a lever 10D. 10E denotes a spring and has a base portion supported on a shaft 10F of the support member 10A. The tip of the spring 10E abuts on the forward upper surface of the cloth presser 10B and serves to energize the cloth presser 10B in a clockwise direction around the shaft 10C. 10G denotes a loop presser, and is rotatably supported by a shaft 10H in a horizontal direction with respect to the cloth presser 10B and is energized in the clockwise direction by means of a spring 10I. The loop presser 10G is constituted such that a tip thereof is positioned below the lower surface of the cloth presser 10B by the function of the spring 10I as shown in FIG. 7 when the presser rod which is not shown is lifted.
FIG. 8 is a plan view showing a throat plate 20 according to the conventional art, and three needle holes 20A for needle location parts through which three needles N for a covering chain stitch penetrate are formed in a central part and a loop guide hole 20B is formed in the forward cloth feeding direction of the needle hole 20A, and the needle hole 20A and the guide hole 20B are caused to communicate through three slits 20C which are parallel with the cloth feeding direction. Two threading pieces 20D are formed by the slit 20C.
Moreover, the throat plate 20 is provided with a needle hole 20E for an over-edge chain stitch and a threading piece 20F on the right side of a portion in which the needle hole 20A is formed.
Furthermore, the throat plate 20 is provided with a cloth feed dog hole 20G from which an accessory feed dog frequently appears on this side and left side in the cloth feeding direction of the needle hole 20A, and a feed dog hole 20J from which a loop feed dog 20H and a main feed dog 20I frequently appear is formed in a rear part in the cloth feeding direction of the needle hole 20A.
Next, functions will be described.
When the sewing machine is driven, the three needles N are vertically moved interlockingly with a main spindle which is not shown, a looper which is not shown is rocked to describe an elliptic locus around the needle, and the accessory feed dog and the main feed dog 20I carry out four motions for cloth feeding.
Consequently, when the cloth presser 10B descends and comes in contact with the upper surface of the throat plate 20 without a cloth put on the lower surface of the cloth presser 10B, a loop is formed between the lower surface of the cloth presser 10B and the upper surface of the throat plate 20 by the needle thread of the needle N and the looper thread of the looper which is not shown and is pressed by the loop presser 10G.
Moreover, when the cloth is present between the lower surface of the cloth presser 10B and the upper surface of the throat plate 20, it is fed by the cloth feed dog in the cloth feeding direction and a stitch is formed on the cloth by the needle thread of the needle N and the looper thread of the looper which is not shown.
However, the conventional art has the following problems.
More specifically, as shown in FIG. 7, when the cloth presser 10B is lifted, the tip of the loop presser 10G protrudes downward from the lower surface of the cloth presser 10B by the function of the spring 10I.
For this reason, when the cloth is to be set between the upper surface of the throat plate 20 and the lower surface of the cloth presser 10B, the cloth abuts on the tip of the loop presser 10G protruding downward from the lower surface of the cloth presser 10B. Consequently, there is a problem in that a cloth setting property is poor and a sewing work efficiency is deteriorated. In particular, this problem is remarkable when a thick cloth is to be set.
Moreover, holding force for pressing and holding a loop against the upper surface of the throat plate 20 by means of the loop presser 10G is determined by the elastic force of the spring 10I. If the holding force of the loop by the elastic force of the spring 10I is small, the loop is pulled in a reverse direction to the cloth feeding direction depending on thread fastening for the needle thread so that the loop cannot be formed stably and continuously.
Moreover, in the case in which a step is made between the lower surface of the loop presser 10G and that of the cloth presser 10B, the loop cannot be held between the lower surface of a loop pressing portion and the upper surface of the throat plate. In order to eliminate the step, a highly developed processing technique is required.
In order to solve the conventional problem, a first aspect of the invention is directed to a loop holding device of a chain stitch sewing machine comprising:
a needle for penetrating through a cloth on a throat plate to be vertically moved interlockingly with a main spindle of the sewing machine, thereby holding a needle thread;
a cloth presser provided on the throat plate and serving to press the cloth;
a looper having a looper thread for reciprocating in such a direction as to cross a cloth feeding direction below the throat plate interlockingly with the main spindle of the sewing machine;
a main feed dog for feeding a loop formed by the needle thread and the looper thread in cooperation of the needle and the looper rearward in the cloth feeding direction; and
a loop engagement member for upward protruding from an upper surface of the throat plate and engaging the loop when the main feed dog is descending from the upper surface of the throat plate.
According to the first aspect of the invention, if the loop presser is brought down from the upper surface of the loop presser when the cloth presser is lifted, nothing protrudes between the upper surface of the throat plate 30 and the lower surface of the cloth presser. Therefore, a cloth setting property between the upper surface of the throat plate 30 and the lower surface of the cloth presser can be improved and the effect of enhancing a sewing work efficiency can be obtained, and particularly, the effect of enhancing a thick cloth setting property can be obtained.
A second aspect of the invention is directed to the loop holding device of a chain stitch sewing machine according to the first aspect of the invention, wherein the loop engagement member is provided between a main feed dog and a needle location part.
According to the second aspect of the invention, it is possible to obtain such an advantage as to more enhance the effect according to the first aspect of the invention.
A third aspect of the invention is directed to the loop holding device of a chain stitch sewing machine according to the first or second aspect of the invention, wherein the loop engagement member can adjust upper and lower positions.
According to the third aspect of the invention, it is possible to regulate the holding force of the loop over the lower surface of the cloth presser by the loop engagement member, thereby corresponding to the strength of thread fastening for the needle thread. Therefore, it is possible to obtain an effect that the loop can be prevented from being pulled in a reverse direction to the cloth feeding direction and can be formed stably and continuously.